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Isle Royale pack down to 2 female wolves

Several members of an Isle Royale wolf pack in this 2006 photo include the immigrant male wolf (the gray wolf in the middle right) along with his radio-collared daughter and mate wolf on the far right. The single male, which crossed to the island in 1997, has 22 offspring, 34 grand-offspring and is responsible for 56 percent of the gene pool among island wolves. (Photo courtesy Michigan Technological University)

The number of wolves roaming on Lake Superior's Isle Royale has dwindled to just 16 with only two breeding females -- a population level researchers say may not be sustainable much longer.

If the two remaining mating females were to die before raising female pups, the wolf population could be headed to extinction.

That's the report released Tuesday from researchers at Michigan Technological University who have been studying moose on the island for 53 years, considered among the longest-running predator-prey studies in the world.

"The situation is kind of precarious," said John Vucetich, the Michigan Tech professor who leads the research effort. "Every wolf has a 25 percent chance of dying in any given year, so we could lose those remaining females at any time."

The 16 wolves counted this winter are down from 19 last year and 24 in 2009.

Once numbering as many as 50, with seven packs, the wolves are down to one pack.

Vucetich said the sex ratio should be close to 50-50 "and it's been 40 years since we only had one pack. So we have three big issues that are working against them."

"But it's always been precarious," said Rolf Peterson, former head of the Isle Royale research who is still involved in the island study, noting that the average population size is only 24.

The scientists acknowledge that National Park Service policy for the island favors a hands-off, natural management. But they say the Park Service should consider introducing wolves to help reduce inbreeding and bolster the population.

"There's no formal policy that says they shouldn't step in toward genetic rescue. But it's an option we think they should at least take a look at," Vucetich said. "Is it better for the wilderness or for the park if wolves go extinct? Or should something be done to keep wolves on the island? We are getting close to that decision."

Isle Royale National Park officials could not be reached Tuesday afternoon for comment.

With no new wolves entering the population, inbreeding appears to be affecting the island wolves' ability to reproduce and thrive. Researchers in 2009 confirmed that inbreeding is causing wolf deformities such as weak vertebrae. A spinal deformity has been found in 100 percent of wolf skeletons tested.

Wolves crossed ice and first came to the island about 1950. Wolf numbers have ranged from a low of 11 in 1993 to a high of 50 in 1980.

Moose numbers up

Scientists say the moose population appears to be slowly recovering after their numbers bottomed out a few years ago. They counted 515 moose during this winter's count, up from 510 last year and the year before.

Moose calves on the island were larger this winter, and the fat content of bone marrow indicates that adult moose are better nourished now. The scientists have spotted three sets of twins in the past two years, the first twins since 2005. Winter ticks, which posed a severe threat to the Isle Royale moose in 2007, have declined significantly since then.

Researchers say moose appear to have hit bottom at 385 in 2007, though their numbers remain less than half their historic, long-term average. Scientists speculate that warmer weather has spurred parasites and other problems for the moose.

"We've been thinking they are about to pull out of their really low period. And the habitat has rebounded, with lower moose numbers, so there's lots of food for them to eat," Vucetich said. "If they don't come back stronger fairly soon, then the impact (from climate change) may be bigger than we had previously thought."

Moose came to the island around 1900, peaking at 2,445 in 1995.

Scientists were on the island from January to March, counting and studying wolves and moose.

Isle Royale, a U.S. National Park, sits about 15 miles from Grand Portage off Minnesota's North Shore and is primarily a wilderness area. It's a nearly controlled natural environment because there is only one predator -- wolves -- and only one major prey -- moose -- with no deer, bear or human hunters involved.